1. Field of the Invention
This invention relates to an electrophotographic reproducing machine.
2. Description of Prior Art
In conventional electrophotographic reproducing machines, a shield plate made of a metal plate is mounted at the upper portion of a machine frame which accommodates therein a photosensitive drum and a plurality of process units, so that the shield plate and the upper portion of the machine frame constitute a housing for an exposure optical system. A movable mount for the exposure optical system is fitted on guide rails fixed to the upper inner face of the machine frame, and a document glass plate is placed on the upper surface of the machine frame in a fixed manner.
In the conventional machine structure thus arranged, therefore, since various constituent members of the exposure optical system are mounted onto the machine frame as the central base, an assembling line for reproducing machines becomes very long and this leads to disadvantages such as an enlargement of facilities and a prolonged time limit of delivery.
Further, a light beam radiated from an exposure lamps leaks through a gap between metal plates, and this requires an additional working step adapted to prevent such leakage of the light beam. Heat within the housing for the exposure optical system is radiated to the peripheral surface of the photosensitive drum by the shield plate made of a metal plate, so that the photosensitive drum will deteriorate in an early time. At the same time, due to less air convection within the housing for the exposure optical system, temperature within the housing is increased, thus resulting in many problems.
Meanwhile, a housing for an exposure optical system in conventional electrophotographic reproducing machines is composed of a shield plate made of a metal plate fixed at the upper portion of a machine frame which accommodates therein a photosensitive drum and a plurality of process units, a lens mounting frame extending in the transverse direction of the machine frame, rails fixed to the inner side face of the machine frame for guiding a movable mount for the exposure optical system, and a black box fixed on the upper face of the shield plate to interrupt external lights. But according to thus structured housing for the exposure optical system, the manufacturing cost is increased due to large number of parts and adjustment as well as shield processing become intricate due to unavoidable errors in machining and assembling with many respective parts. With this, it is difficult to achieve reduction in the manufacturing cost as a result of mass production. Further, the housing for the exposure optical system is required to be assembled onto the machine frame which is running forward on the assembling line, so it is also difficult to conduct preassembling of the exposure optical system.
Meanwhile, in a movable mount for conventional electrophotographic reproducing machines, there has been used a current collector in slide-contact with an electrode plate as a stationary portion of the machine in order to feed an exposure lamp and other parts with current. The prior current collector includes a coil spring interposed between a current applying metal plate and a current collecting brush, thereby to effect the electrical coupling between both members. This results in several problems such as early fatigue of the coil spring due to its heating, occurrence of noise and failed conducting.
Moreover, when feeding electrical power to the movable mount mounting thereon the exposure lamp, the current collecting is usually effected in a system wherein an electrode line is laid along running rails for the movable mount through an insulative base plate, such that a current collecting brush provided on the movable mount is brought into slide-contact with the electrode line. However, the electrode line in the prior art is formed of a long and narrow printed board or the like and this printed board is fixed to the running rails for the movable mount, thus resulting in the intricate assembling process.
Meanwhile, a document glass plate for electrophotographic reproducing machines is required to be held precisely in parallel with respect to the optical axis of an exposure optical system. In the past, the document glass plate has been seated in an upper flange of a machine frame constituting a housing for the exposure optical system onto which are mounted constituent members of the exposure optical system, so that it is difficult to hold the aforesaid precise parallel relationship in terms of a limit in machining accuracy just by directly seating the document glass plate in the upper flange. From this reason, when mounting the document glass plate onto the machine frame, a spacer with an appropriate thickness is interposed heretofore between the upper flange and the document glass plate, thereby to attain the aforesaid parallel relationship. But such adjustment at the time of assembling requires highly experienced and intricate work and hence it is not suitable for mass production.
Furthermore, as well known, in an exposure optical system for electrophotographic reproducing machines, a lens plate is disposed within a shield box in the transverse direction and a mounting flange of a projection lens is screwed to the lens plate.
But there is a variation in the respective projection lenses manufactured and, particularly, resolving power of an image takes various values depending on directions within the image. Thus, the above-mentioned structure in which the projection lens is screwed to the lens plate using the mounting flange can not ensure that a portion of the projection lens having the highest resolving power is utilized for the belt-like image having passed through a slit.
Also, as well known, focus adjustment of the projection lens is carried out using a spacer with a desired thickness which is interposed between the projection lens and the lens plate. In such conventional focus adjustment structure, however, mounting screws have to be loosened every when inserting one of plural spacers different in thickness thereof, and this results in the intricate adjustment work. Further, since the mounting screws are fastened in the direction corresponding to the depthwise direction of the spacer, the projection lens is made to move along the optical axis of the projection lens during the fastening process, whereby such adjustment work requires highly experienced skill.
In addition, an exposure optical system for reproducing machines generally include a shield box for shielding a light beam having passed through the projection lens from external lights, and the shield box mounts therein a mirror adapted to reflect the incident light from the projection lens toward a photosensitive drum.
Heretofore, an all-metal frame has been usually employed, so it was not unavoidable, for example, that there occurs some error in a distance between the portion for mounting a barrel of the projection lens and the portion for mounting the reflection mirror, thus leading to a problem that a fairly large amount of time is required for adjustment of such error. This results from errors in dimensions of the metal frame and in mounting thereof, therefore the metal frame itself can not contribute to adjustment of errors. There has been also known a mounting structure for the reflection mirror such that the mounting surface of the shield box is finished to a mirror surface and then the mirror is seated on the mounting surface. But it is very difficult to precisely finish the mounting surface with respect to the optical axis of the projection lens as well as a relationship between the optical axis and the photosensitive drum. Therefore, a spacer or the like is interposed between the mounting surface and the mirror in the prior art, thereby to secure the satisfactorious accuracy in positional relationships, but this adjustment is an intricate work which requires special skills and much time.
Meanwhile, the shield box is constituted by metal plates disposed on a shield plate at the bottom portion of a housing for the exposure optical system. A top plate of the shield box is formed of a draw lid so as to allow a mirror mounted within the shield box to be cleaned.
However, such conventional structure has encountered a difficult in shielding between the shield box body and the draw lid completely. Penetration of stray lights from surroundings after regular assembling requires additional machining work to achieve complete shielding. Since the shield box must undergoes the plate work, the manufacturing cost is highly increased.
Further, as mentioned above, in conventional electrophotographic reproducing machines, a shield plate made of a metal plate is mounted at the upper portion of a machine frame which accommodates therein a photosensitive drum and a plurality of process units, so that the shield plate and the upper portion of the machine frame constitute a housing for an exposure optical system. A movable mount for the exposure optical system is fitted on guide rails fixed to the upper portion of the machine frame, and a document glass plate is placed on the upper surface of the machine frame in a fixed manner.
According to such machine structure, however, assembling and adjustment works become very intricate and hence the manufacturing cost is highly increased. In order to solve this problem, it may be advisable to adopt such a structure that the housing for the exposure optical system is resin-molded and thus obtained resin housing is mounted onto the machine frame. But this structure is accomplished with another problem how to coincide the optical axis of the machine frame with that of the housing for the exposure optical system.